text: /*
   * Copyright 2017 Facebook, Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #pragma once
  
  #include <folly/Portability.h>
  #include <folly/Try.h>
  #include <functional>
  
  namespace folly {
  
  // forward declaration
  template <class T>
  class SemiFuture;
  template <class T> class Future;
  
  namespace futures {
  namespace detail {
  template <class T>
  class FutureBase;
  struct EmptyConstruct {};
  template <typename T, typename F>
  class CoreCallbackState;
  } // namespace detail
  } // namespace futures
  
  template <class T>
  class Promise {
   public:
    static Promise<T> makeEmpty() noexcept; // equivalent to moved-from
  
    Promise();
    ~Promise();
  
    // not copyable
    Promise(Promise const&) = delete;
    Promise& operator=(Promise const&) = delete;
  
    // movable
    Promise(Promise<T>&&) noexcept;
    Promise& operator=(Promise<T>&&) noexcept;
  
    /** Return a SemiFuture tied to the shared core state. This can be called only
      once, thereafter FutureAlreadyRetrieved exception will be raised. */
    SemiFuture<T> getSemiFuture();
  
    /** Return a Future tied to the shared core state. This can be called only
      once, thereafter FutureAlreadyRetrieved exception will be raised.
      NOTE: This function is deprecated. Please use getSemiFuture and pass the
            appropriate executor to .via on the returned SemiFuture to get a
            valid Future where necessary. */
    Future<T> getFuture();
  
    /** Fulfill the Promise with an exception_wrapper */
    void setException(exception_wrapper ew);
  
    /** Fulfill the Promise with an exception_ptr, e.g.
      try {
        ...
      } catch (...) {
        p.setException(std::current_exception());
      }
      */
    FOLLY_DEPRECATED("use setException(exception_wrapper)")
    void setException(std::exception_ptr const&);
  
    /** Fulfill the Promise with an exception type E, which can be passed to
      std::make_exception_ptr(). Useful for originating exceptions. If you
      caught an exception the exception_wrapper form is more appropriate.
      */
    template <class E>
    typename std::enable_if<std::is_base_of<std::exception, E>::value>::type
    setException(E const&);
  
    /// Set an interrupt handler to handle interrupts. See the documentation for
    /// Future::raise(). Your handler can do whatever it wants, but if you
    /// bother to set one then you probably will want to fulfill the promise with
    /// an exception (or special value) indicating how the interrupt was
    /// handled.
    void setInterruptHandler(std::function<void(exception_wrapper const&)>);
  
    /// Sugar to fulfill this Promise<Unit>
    template <class B = T>
    typename std::enable_if<std::is_same<Unit, B>::value, void>::type
    setValue() {
      setTry(Try<T>(T()));
    }
  
    /** Set the value (use perfect forwarding for both move and copy) */
    template <class M>
    void setValue(M&& value);
  
    void setTry(Try<T>&& t);
  
    /** Fulfill this Promise with the result of a function that takes no
      arguments and returns something implicitly convertible to T.
      Captures exceptions. e.g.
  
      p.setWith([] { do something that may throw; return a T; });
    */
    template <class F>
    void setWith(F&& func);
  
    bool isFulfilled() const noexcept;
  
   private:
    typedef typename Future<T>::corePtr corePtr;
    template <class>
    friend class futures::detail::FutureBase;
    template <class>
    friend class SemiFuture;
    template <class>
    friend class Future;
    template <class, class>
    friend class futures::detail::CoreCallbackState;
  
    // Whether the Future has been retrieved (a one-time operation).
    bool retrieved_;
  
    // shared core state object
    corePtr core_;
  
    explicit Promise(futures::detail::EmptyConstruct) noexcept;
  
    void throwIfFulfilled();
    void throwIfRetrieved();
    void detach();
  };
  
  } // namespace folly
  
  #include <folly/futures/Future.h>
  #include <folly/futures/Promise-inl.h>
  